static <A> A shallowClone(A o) {
  ret (A) shallowClone_impl(o);
}

static <A> A shallowClone(A o, A emptyClone) {
  ret copyFields(o, emptyClone);
}

static O shallowClone_impl(O o) {
  if (o == null)
    return o;
    
  if (o instanceof List)
    ret cloneList((List) o);

  if (o cast Map) ret cloneMap(o);

  if (o instanceof String || o instanceof Number || o instanceof Boolean)
    return o;
    
  if (o instanceof Object[]) {
    Object[] l = (Object[]) o;
    ret l.clone();
  }
  
  // clone an arbitrary custom object
  
  O clone;
  if (o cast IMakeEmptyClone)
    clone = o.makeEmptyClone();
  else
    clone = nuEmptyObject(o.getClass());

  //print("Cloning custom: " + o);
  copyFields(o, clone);
  ret clone;
}